

583.123 

 Nlloaf 

 I 1992 1 



MONTANA STATE LIBRARY 



3 0864 0010 3930 7 



WU^lZhTUj 



The Occurrence of Arabis fecunda 

 on BLM Lands in the Humbug Spires Area, Silver Bow County 



Introduction 



Sapphire rockcress ( Arabis fecunda Rollins) is a rosette-forming perennial in the 

 Mustard Family (Brassicaceae). This recently described species (Rollins 1984) is endemic to 

 highly calcareous, azonal soils in the foothills of the Sapphire Range in Ravalli County and in 

 the Pioneer Range in Beaverhead and Silver Bow counties, Montana (Lesica 1985, 

 Schassberger 1988). Arabis fecunda occurs on eroding slopes with low vascular plant density 

 but often a relatively high cover of cryptogamic soil crust (Lesica and Shelly 1992). Arabis 

 fecunda is a candidate for listing as a threatened or endangered species by the U.S. Fish and 

 Wildlife Service (USDI, FWS 1990) and is considered threatened in Montana (Lesica and 

 Shelly 1991). 



In 1991 a population of A^ fecunda was located in the Humbug Spires area of 

 southern Silver Bow County (R. DeVelice, pers. com.). This population was the east of any 

 previously known sites for the species. The purpose of this study was to survey lands 

 administered by the Bureau of Land Management (BLM) in the southern portion of Silver 

 Bow County to locate other populations of this rare plant. 



Methods 



I obtained information on the geology of the area from the geologist for the Butte 

 District of Deerlodge National Forest. I used this information, aerial photos and USGS 

 topographic maps to determine areas likely to harbor populations of Arabis fecunda . I then 

 searched these areas on foot to locate populations. The area covered by this study is 

 presented in Figure 1. 



Results 



I located four populations of Arabis fecunda on lands administered by BLM in the 

 Humbug Spires area (Figs. 1-4). Sites on the west slope of the Humbug Spires at 6,000- 

 6,900 ft are dominated by Cercocarpus ledifolius . Juniperus scopulorum and Agropyron 

 spicatum . Each of these sites, including the one located in 1991, contain at least 5,000- 

 10,000 A,, fecunda plants. The site on the southeast side of the Humbug Spires at 6,700- 

 6,900 ft. is dominated by herbaceous vegetation, Agropyron spicatum . Koeleria crista ta . 

 Phlox muscoides and other cushion plants. There are an estimated 1,000-5,000 A., fecunda 

 plants at this site. 



3TC7E DOCUMENTS COLLECTION 





i 



ma L 



ft *"= 



- 



i 





: 'd \i H 







MONTANA STATE LIBRARY 



1515 E. 6th AVE. 

 HELENA, MONTANA 59620 



